I can't say for certain, but if the thieves targeted certain trains and accessories and left others, ended up taking items that were the most expensive, then it is unlikely these were common thieves on a smash and grab. They could be thieves knowledgeable about the value of certain toy trains, they could be people who were asked to steal certain items that a collector wanted, they could be collectors themselves (though I doubt it is the last one). If it was someone breaking in who didn't know, they would do a smash and grab, not pick out certain items, smash and grab artists get as much as they can, figuring they can fence it based on the quantity.
As far as being able to find the perpetrators, it may not be easy to trace this, unless these were really rare items, where let's say there are only a couple known in existence, that could be true, since if someone attempts to sell something rare, it is likely whoever they sell it to will know it is rare. But it isn't like there is a registry of toy trains, and they don't really have identifying marks on them that would make tracing them easy (there might be a serial number of some of the stuff, but was it recorded).
It could be that the thieves, unlike the impression I am getting, basically grabbed a lot of stuff fast, then it could be morons thinking "old things in a museum=money", of course, and you might see them getting busted when they try to sell it to a store or something like that, but I suspect based on what little I have seen that this may have been a targeted theft of specific stuff.
While in many ways it is different than toy trains, in the art world and rare musical instruments thefts are generally targeted, thieves steal stuff knowing there is a private collector who wants the piece or item for his/her collection, because stealing such items without knowing someone wants it and will buy it is too risky. If you steal a rare violin, like a stradiverius, the minute they tried to sell that to a shop or tried to sell it at auction, they would be busted, because strads are all accounted for, they are well known; if you tried to steal a valuable painting and tried to sell it, it would get you busted, for the same reasons, it is impossible to liquidate it, unless you have a collector willing to pay enough to make it worth the risk.